Dr. Bill Elliott: Smoking pot when young poses brain risks

MARIJUANA USE has never been so popular in America. More teens, up to 23 percent, have tried pot in the past month — more than have smoked a cigarette over that same time frame. Pot is now the most popular illicit drug in the world, and the majority of Americans favor its legalization for recreational as well as medicinal use.

But there is a growing body of research that cannabis (the medical term for marijuana) is not as benign as we had once thought. There is evidence that long-term heavy cannabis use may cause persistent neuropsychological impairment beyond just the period of being high. Some studies even show heavy cannabis users performing worse on standardized psychological testing months after stopping the drug.

Now a new, highly publicized study from the National Academy of Sciences raises the level of concern for our children. Researchers from Duke University looked at data from a group of more than 1,000 children in a New Zealand small town — following them from birth to age 38.

Marijuana use in New Zealand, especially in the 1970s and '80s, was more prevalent than in this country and the potency of the drug was about the same as pot found here. The subject's cannabis use was measured at age 18 and continued through age 38. The researchers found that starting regular cannabis use prior to age 18 was associated with neuropsychological decline later in life — specifically a decline in IQ of up to 8 points. This finding was consistent regardless of years of education. The loss of IQ points persisted years after quitting cannabis but only for those who started smoking at a young age. Losses in IQ points were not noted in subjects who started smoking marijuana after age 18.

These findings are suggestive of a neurotoxic effect of cannabis on the adolescent brain. In other words, as children are growing and the brain is developing, cannabis may cause permanent damage that results in decreased long-term intelligence and changes in neuropsychological function.

This is a particularly scary scenario since studies are showing that fewer adolescents believe that regular pot smoking is harmful to their health. Studies also show that teenagers are starting cannabis at younger ages, and more adolescents are using cannabis on a regular basis — even daily.

The authors of the study suggest that more effort should be made to delay the onset of cannabis use by young people, and young users of the drug should be encouraged to quit. Quitting, especially at a young age, may have beneficial effects, preventing additional damage.

This study, plus others that suggest cannabis may cause brain injury to young pot smokers, has shown an increased vulnerability to severe psychological problems, even psychosis. All this suggests that for young cannabis users, the drug is not as benign as we once thought.

Again the data from a New Zealand study found that none of this applied to adults. Starting regular cannabis use after the brain had fully developed was not associated with long-term loss of IQ points. Still, we need to always be open to new data and question the status quo, even if the status quo today is yesterday's "counter culture."

If you think you teenager is smoking pot, take action. Stay involved in their lives. Channel them to positive activities. Be aware of their friends. Most of all, talk to them. If you think their use is chronic, or even daily, then seek help.

Dr. Bill Elliott is an internist at Kaiser Novato and an assistant clinical professor of medicine at UCSF. His column appears every third Monday.